将得分发布到Facebook时出现运行时错误。

当我试图将得分发布到 Facebook 时，我收到以下错误：

运行时错误... \main.lua:22:尝试调用全局变量'score'(数字值) 堆栈回溯: [C]：在函数'score'中

我真的不明白为什么它无法工作。 完整的代码是：

local facebook = require ("facebook")
local json = require ("json")

keeping_score = true
score = 1000

keeping_score = true
local scoreText = display.newText( "Score: " .. score, 20, 20,nil, 20)
scoreText:setTextColor(255,255,255)

print("" .. score)

--Facebook function
local faceListener = function (event)
   local faceMessage = {
                name = "Name",
                link = "http://www.site.com",
                message = "我在玩Name时获得了".. score"的分数，立即免费下载iPhone和Android：www.site",
                caption = "你能打败我的分数吗?".. score,
                description = "Name在此，立即免费下载iPhone和Android：www.site",
                picture = "http://cdn01.androidauthority.com/wp-content/uploads/2011/03/Google-Logo.jpg",
                actions = json.encode( { name = "Name", link = "http://www.site.com" } )
                          }
   --检查登录情况，如果一切正常，则调用发布faceMessage。
   if event.type == "session" then
      if event.phase == "login" then
          facebook.request( "me/feed", "POST", faceMessage )
      end
   end
end

local faceFunc = function ()
      facebook.login("appID", faceListener {"publish_stream"} )
end

--激活发布到Facebook的按钮
local facebutton = display.newRect (0, 0, 50, 50)
facebutton.x = display.contentWidth/2; facebutton.y = display.contentHeight/2
facebutton:addEventListener("tap", faceFunc)

有什么解决方法吗?